Identifying and monitoring connections in an optical system

ABSTRACT

Techniques are provided for identifying and monitoring connections in an optical system. A plurality of optical ports is configured to receive a plurality of optical links that couple with one or more remote optical devices. At least one light source generates identification (ID) signals. At least one optical element configured to direct the ID signals into transmission paths from the source optical device to the remote optical device/s over the plurality of optical links. The remote optical device/s include one or more optical elements that direct the ID signals through a set of WDM filters and returns the ID signals. At least one optical element directs returned ID signals to an optical channel monitor. At least one microprocessor configured to execute control instructions to generate the ID signals and process one or more outputs of the optical channel monitor in response to the returned ID signals to identify the plurality of optical links.

RELATED APPLICATIONS

The present application claims priority to Chinese Patent ApplicationNo. 202110075711.5 filed on Jan. 20, 2021 which is incorporated byreference in its entirety.

TECHNICAL FIELD

The present disclosure generally relates to optical systems, and relatesmore specifically to the identification and monitoring of connectionsbetween optical devices.

BACKGROUND ART

The approaches described in this section are approaches that could bepursued, but not necessarily approaches that have been previouslyconceived or pursued. Therefore, unless otherwise indicated, it shouldnot be assumed that any of the approaches described in this sectionqualify as prior art merely by virtue of their inclusion in thissection.

Optical networks are used for many applications, such as communication,measurement, monitoring, energy delivery, and other applications.Optical networks typically offer high-speed voice, video, and datatransmission between providers and homes, businesses, and othernetworks. In an optical network, optical links connect two or moreoptical devices. An optical link includes a communication mediumconnected to a device that enables optical communication over thecommunication medium, such as one or more optical fibers.

The optical link configurations in an optical network may becomecomplex. For example, one optical device may be connected with one ormultiple other optical devices, with one or multiple optical linksbetween each optical device pair. Optical devices may be located indifferent slots of the same optical network device shelf, a differentshelf of same network device rack, different locations of same site,and/or different sites. For example, some optical devices may be locatedremotely from a site controlled by an operator of an optical network,such as to be physically close to a user location. Optical patch panelsor optical shuffle boxes may be employed in managing optical connectionsat a site.

A wavelength-division multiplexing (“WDM”) system is often employed inan optical network to handle routing. A WDM system typically multiplexesa number of optical signals with different wavelengths so that multipledistinct signals may travel over a single optical fiber. Because thefiber can simultaneously carry multiple signals, WDM can increase thecomplexity of optical links at a node of the network when the multiplesignals are separated.

Optical links are often physically connected using cables on an ad hocbasis, making cable management and/or mapping difficult. Identificationof a connection path, such as during device setup, configuration, and/orreconfiguration, may be a complex task. It may also be challenging tomonitor the operation of optical links, such as to detect brokenconnections and/or degradation.

A typical solution may involve lasers and photodetectors withcomplicated algorithms in order to identify and/or monitor optical linksat a remote site, which may require complex powered electrical circuitsand powerful CPU to handle identification, monitoring, and/orcommunication with network controller. However, a remote optical devicemay be passive, without electrical circuitry and with no access toelectrical power. For example, passive optical devices may appear atremote sites that are geographically distant from a connected site withpowered optical device.

SUMMARY

The appended claims may serve as a summary.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 illustrates an optical system in an example embodiment;

FIG. 2 illustrates an optical system with an ID block in a sourceoptical device and a remote ID block in a remote optical device in anexample embodiment;

FIGS. 3A-3B illustrate sets of WDM filters in an example embodiment;

FIG. 4 illustrates an optical system with a monitor block in a sourceoptical device and a remote monitor block in a remote optical device inan example embodiment;

FIG. 5 illustrates an optical system with a monitor block for a sourceoptical device and a remote monitor block for a remote optical device inan example embodiment;

FIG. 6 illustrates an optical system with an optical add-dropmultiplexer (OADM) node in an example embodiment;

FIG. 7 illustrates a direction device and an add-drop group device in anOADM node in an example embodiment;

FIG. 8 illustrates a direction device and an add-drop group device in anOADM node that implements an ID mechanism in an example embodiment;

FIG. 9 illustrates a direction device and an add-drop group device in anOADM node that implements a monitor mechanism in an example embodiment;

While each of the drawing figures illustrates a particular embodimentfor purposes of illustrating a clear example, other embodiments mayomit, add to, reorder, or modify any of the elements shown in thedrawing figures. For purposes of illustrating clear examples, one ormore figures may be described with reference to one or more otherfigures. However, using the particular arrangement illustrated in theone or more other figures is not required in other embodiments.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In the following description, numerous specific details are set forth inorder to provide a thorough understanding of the present disclosure. Itwill be apparent, however, that the present disclosure may be practicedwithout these specific details. The detailed description that followsdescribes exemplary embodiments and the features disclosed are notintended to be limited to the expressly disclosed combination(s).Therefore, unless otherwise noted, features disclosed herein may becombined to form additional combinations that were not otherwise shownfor purposes of brevity.

It will be further understood that: the term “or” may be inclusive orexclusive unless expressly stated otherwise; the term “set” may comprisezero, one, or two or more elements; the terms “first”, “second”,“certain”, and “particular” are used as naming conventions todistinguish elements from each other, and does not imply an ordering,timing, or any other characteristic of the referenced items unlessotherwise specified; the term “and/or” as used herein refers to andencompasses any and all possible combinations of one or more of theassociated listed items; that the terms “comprises” and/or “comprising”specify the presence of stated features, but do not preclude thepresence or addition of one or more other features.

This document generally describes systems, methods, devices, and othertechniques for identifying and monitoring connections in an opticalsystem. An optical system includes one or more source optical devicesand one or more remote optical devices that implement an identificationmechanism and/or a monitor mechanism.

To implement the identification mechanism, a source optical deviceincludes an identification (ID) block comprising optical elements thatperform identification of one or more connections to one or more remoteoptical devices. The one or more remote optical devices each include aremote ID block comprising one or more optical elements. ID signalsgenerated at the source optical device are transmitted to the one ormore remote optical devices, processed by the remote ID block, andtransmitted back to the source optical device, where the ID blockidentifies the one or more connections based on the returned ID signals.The ID signals generated at the source optical device for identificationbelong to a set of ID wavelengths λ_({ID}). In some embodiments,λ_({ID}) does not overlap with a set of service wavelengthsλ_({service}), and the identification mechanism is not used duringnormal operation of the source optical device and the remote opticaldevice.

To implement the monitor mechanism, a source optical device includes amonitor block comprising optical elements that evaluate connectivity ofone or more connections between the source optical device and one ormore remote optical devices. The one or more remote optical devices eachinclude a remote monitor block comprising one or more optical elements.Monitor signals generated at the source optical device are transmittedto the one or more remote optical devices, processed by the remotemonitor block, and transmitted back to the source optical device, wherethe monitor block evaluates the connectivity of the one or moreconnections based on the returned monitor signals. The monitor signalsgenerated at the source optical device may have a reference wavelengthλ_(r). In some embodiments, λ_(r) does not overlap with a set of servicewavelengths λ_({service}), and the monitoring mechanism is used duringnormal operation of the source optical device and the remote opticaldevice.

In some embodiments, the remote ID block/s and/or the remote monitorblock/s only include passive elements that do not require electronicelements and/or electronic power. In this manner, only purely passiveoptical circuits are deployed in the remote optical device/s that can betested using the ID mechanism and/or the monitor mechanism. Additionalfeatures and advantages are apparent from the specification and thedrawings.

FIG. 1 illustrates an optical system in an example embodiment. Theoptical system 100 includes an optical network with one or more sourceoptical devices 102 and one or more remote optical devices 106-108. Asused herein, the term “optical device” refers to optical equipment withone or more optical ports to communicatively couple the optical deviceto another device so that optical signals can travel over acommunication link between the optical devices. An optical device may bea standalone device, and/or may include two or more optical devicecomponents.

The source optical device 102 communicates with the one or more remoteoptical devices 106-108 via one or more optical links 1-i. A sourceoptical device 102 may be coupled with a particular remote opticaldevice 106-108 by one or multiple optical links. An optical link mayinclude a transmitter, receiver, and cable assembly that can transmitinformation between two points. An optical link may includeunidirectional or bidirectional fibers. For example, optical link 1includes two fibers used for unidirectional communication, while opticallink 3 includes one fiber used for bidirectional communication. As usedherein, a fiber within an optical link is referred to as an optical linkcomponent. An optical link may include one or more cables that terminatewith one or more optical connectors designed to mate with an opticalport of an optical device.

The source optical device 102 may be configured to perform one or morefunctions in conjunction with one or more remote optical devices106-108. The function/s are carried out by a function block 104 at thesource optical device 102 and one or more function blocks 110-112 at theremote optical devices 106-108. As used herein, an optical block, suchas function blocks 104 and 110-112, is a set of one or more opticalelements that generate and/or process one or more optical signalsrelated to a particular function. In some embodiments, the sourceoptical device 102 is a direction device in an OADM node, and the remoteoptical devices 106-108 are add-drop group devices in the OADM node.

Function block 104 generates service signals having frequencies selectedfrom a set of service wavelengths λ_({service}) that are transmitted toone or more remote optical devices 106-108 over the one or morecommunication links 1-i. In some embodiments, λ_({service}) includeswavelengths in a particular communication band, such as the O-band,E-band, S-band, C-band, L-band, 850-nm-band, U-band, and/or anothercommunication band. A channel refers to an optical signal transmitted ata particular wavelength. As used herein, the term “transmission path”refers to the path of service signals from a function block 104 of asource optical device 102 to a function block 112 of a remote opticaldevice 108. As used herein, the term “receiving path” refers to the pathof service signals from a function block 112 of a remote optical device108 to a function block 104 of a source optical device 102. Atransmission path and/or a receiving path may travel over an opticallink. Transmission path i carries service signals of a particularservice wavelength λ_(i) from W₁ to X₁ over optical link i. Receivingpath i carries service signals of λ_(i) from Z₁ to Y₁ travel overoptical link i.

In some embodiments, the source optical device 102 is configured toidentify optical connections at one or more remote optical devices106-108. For example, the source optical device 102 may determine thatsignals of a particular wavelength travel over a particular opticallink. In some embodiments, the source optical device 102 identifies aplurality of optical connections to a plurality of remote opticaldevices 106-108. The source optical device 102 may include anidentification (ID) block 114 that includes one or more optical elementsthat identify connections to one or more remote optical devices 106-108.The ID block 114 transmits identification (ID) signals havingfrequencies selected from a set of wavelengths λ_({ID}) to one or moreremote optical devices 106-108, such as by directing the ID signals intotransmission path i at B₁. A remote ID block 116 at a remote opticaldevice 108 processes the ID signals from the ID block 114 and transmitsthe returned ID signals back to the ID block 114. At the remote opticaldevice 108, ID signals from transmission path i are directed to theremote ID block 116 at G₁, and returned ID signals from the remote IDblock 116 are directed to the receiving path at H₁. The returned IDsignals are directed from the transmission path i to the ID block 114 atM₁.

The term “identification mechanism” is used herein to refer to thecombination of the ID block 114 at the source optical device 102 and theremote ID block 116 at one or more remote optical devices 108 opticallyconnected to the source optical device. The identification mechanism isdescribed in greater detail hereinafter.

Alternatively and/or in addition, the source optical device 102 may beconfigured to monitor optical connections at one or more remote opticaldevices 106-108. For example, the source optical device 102 may includea monitor block 118 that includes one or more optical elements thatmonitor connections between the source optical device 102 and one ormore remote optical devices 106-108, such as to evaluate connectivity ofoptical links. The monitor block 118 transmits monitor signals havingone or more reference frequencies of wavelength λ_(r) to one or moreremote optical devices 106-108, such as by directing the monitor signalsinto transmission path i at Pi. A remote monitor block 120 at a remoteoptical device 108 processes the monitor signals from the monitor block118 and transmits the returned monitor signals back to the monitor block118. At the remote optical device 108, monitor signals from transmissionpath i are directed to the remote monitor block 120 at E₁, and returnedmonitor signals from the remote monitor block 120 are directed to thereceiving path at F₁. The returned monitor signals are directed from thetransmission path i to the monitor block 118 at K₁.

The source optical device 102 may include one or more microprocessors150. The microprocessor/s 150 may perform one or more computationsrequired by function block 104, ID block 114, and/or monitor block 118.In some embodiments, the microprocessor/s 150 execute one or morecontrol instructions to carry out one or more control processes. Thecontrol instructions may include hard-coded instructions, firmware,and/or software. In some embodiments, the microprocessor/s 150 executeinstructions for a ID control process to generate ID signals, andprocess measurements of returned ID signals to generate outputcomprising the identity one or more optical links to the remote opticaldevices 106-108. In some embodiments, the microprocessor/s 150 executeinstructions for a monitor control process to generate monitor signals,and process measurements of returned monitor signals to generate outputcomprising the health one or more connections to one or more remoteoptical devices 106-108.

The term “monitor mechanism” is used herein to refer to the combinationof the monitor block 118 at the source optical device 102 and the remotemonitor block 120 at one or more remote optical devices 108 opticallyconnected to the source optical device. The monitor mechanism isdescribed in greater detail hereinafter.

In an optical system, a source optical device 102 and one or moreconnected remote optical devices 106-108 may implement both theidentification mechanism and the monitor mechanism, or may independentlyimplement either the identification mechanism or the monitor mechanism.Different source optical devices in the same optical system mayimplement none, one, or both of the identification mechanism and/or themonitor mechanism. In some embodiments, the source optical device 102 isa direction device in an optical add-drop multiplexer (OADM) node, andeach add-drop group device in the OADM node implements theidentification mechanism, the monitor mechanism, or both theidentification mechanism and the monitor mechanism.

For ease of illustration, aspects described herein with respect to aparticular source optical device, a particular remote optical device,and/or a particular optical link may apply to one or more other sourceoptical devices, remote optical devices and/or optical links. Forexample, an optical system may include one or multiple source opticaldevices; a source optical device may communicate with a remote opticaldevice over one or multiple optical links; and/or a source opticaldevice may communicate with one or multiple remote optical devices.Furthermore, the techniques for identification and monitoring may beapplied to one optical link, multiple optical links, and/or all opticallinks from a source optical device. While one or more specific elementsmay be shown in a particular embodiment, other elements andconfigurations may provide equivalent functionality without departingfrom the spirit or the scope of this disclosure.

FIG. 2 illustrates an optical system with an ID block in a sourceoptical device and a remote ID block in a remote optical device in anexample embodiment. The optical system 200 includes a source opticaldevice 202 and a remote optical device 208 connected by an optical linki. A transmission path i from W₂ to X₂ carries service signals from afunction block 204 of the source optical device 202 to a function block212 of the remote optical device 208, and a receiving path i from Z₂ toY₂ carries service signals from the function block 212 of the remoteoptical device 208 to the function block 204 of the source opticaldevice 202 using a particular service wavelength of a set of servicewavelengths λ_({service}).

The source optical device 202 includes an ID block 214 that identifiesone or more connections at one or more remote optical devices. Theremote optical device 208 includes a remote ID block 216. As previouslynoted, a remote ID block may be present in one or multiple remoteoptical devices connected to the source optical device 202. Furthermore,multiple remote ID blocks may be present in a remote optical device 208.

The ID block 214 transmits ID signals over transmission path i using aset of ID wavelengths λ_({ID}). At A₂, a light source 220 generateslight of the set of wavelengths λ_({ID}). In some embodiments, the lightsource 220 includes one or more broadband light sources, one or moretunable lasers, one or more diodes such as light-emitting diodes (LEDs)and laser diodes (LDs), and/or one or more other light sources that canprovide λ_({ID}) light. In some embodiments, the light source 220 is alight source that exists for another purpose in the source opticaldevice 202, such as a light source that belongs to function block 204.

The ID signals are directed into transmission path i at B₂ using one ormore elements 222-224. For example, element 224 may be a splitter and/orswitch, a multiplexer, or another optical element. In some embodiments,the light source 220 generates λ_({ID}) light that is directed intotransmission paths that travel over one or more other optical links. Forexample, element 222 may be a switch element and/or splitter elementthat transmits light to one or more other transmission paths, such asbut not limited to a transmission path that travels over optical link 2,using one or more elements 242.

At G₂, the ID signals are directed into a bypass path from G₂ and H₂ byusing an element 226 that can direct the ID signals into the bypasspath, such as a switch, or another optical element at G₂. In someembodiments, the bypass path is only enabled when identification ofoptical links is performed for the optical system 200. In such cases,element 226 may be a switch without affecting the transmission ofservice signals during normal operation of function block 204 andfunction block 212.

The ID signals transmitted over transmission path i enter the bypasspath G₂−H₂ and travel to a set of wavelength-division Multiplexing (WDM)filters 228. Each WDM filter of the set of WDM filters 228 can eitherpass or block a different wavelength. The set of WDM filters 228 can beused in different combinations. When the set of WDM filters includes amaximum number of different wavelength filters l, and a maximum numberof filters to “build such Optical ID Block” is k (k<=l), the totalnumber of unique identifiers (IDs) that can be created by “such OpticalID Block” will be equal to C_(l) ^(k)+C_(l) ^(k-1)+ . . . +C_(l) ¹. Forexample, if the set of WDM filters has 400 GHz channel spacing in atypical C band with 4 THz total bandwidth, then the set of WDM filterscan have a maximum of l=10 filters with different wavelength (4 THz/400GHz). If only one filter is used to build the “Optical block” (k=1),then 10 optical links can be identified. If up to two filters are usedto “build the Optical block (k=2), then 55 optical links can beidentified (C₁₀ ²+C₁₀ ¹=45+10=55). Based on the maximum connectivity ofthe source optical device 202, a minimum number of filters needed can bedetermined to ensure every connection can be uniquely identified amongall connections from the source optical device 202 to the remote opticaldevice/s 208.

In some embodiments, the set of WDM filters 228 and/or the remote IDblock 216 is a pluggable component in the remote optical device 208.When the set of WDM filters 228 and/or the remote ID block 216 is apluggable component, the number of WDM filters can be changed, such asto accommodate a greater number of remote optical devices 208identifiable by the source optical device 202.

FIG. 3A illustrates a configuration for a set of WDM filters (e.g. setof WDM filters 228) in a remote ID block (e.g. remote ID block 216) inan example embodiment. A set of WDM filters 328 in a bypass path (e.g.G₂-H₂) includes one or multiple optical notch filters which can blocksignals of different wavelengths (λ_(i), λ_(j), λ_(k)). The filters areplaced in series, and one or a series of wavelengths will be blocked iflight pass through the set of WDM filters 328.

FIG. 3B illustrates a configuration for a set of WDM filters (e.g. setof WDM filters 228) in a remote ID block (e.g. remote ID block 216) inan example embodiment. A set of WDM filters 358 in a bypass path (e.g.G₂-H₂) includes one or multiple optical band pass filters, which caneach pass signals of different wavelengths (λ_(i), λ_(j), λ_(k), λ_(m)).The filters are cascaded together, and one or a series of wavelengthswill be passed while rest will be blocked if light pass through thisblock.

Returning to FIG. 2 , the ID signal is directed into the receiving pathi at H₂. at M₂, one or more elements 232-234, such as one or moresplitters, filters, demultiplexers, and/or other optical modules, directthe returned ID signals from the receiving path i to a set of one ormore elements 236-238 of an optical channel monitor (OCM) 240. The OCM240 measures properties of returned ID signals, such as the wavelengthof a particular received signal. In some embodiments, the OCM 240includes a tunable filter 236 and a photodetector 238. The tunablefilter 236 and photodetector 238 are integrated to perform opticalwavelength channel monitoring. The OCM 240 allows the ID block 214 todetermine which wavelength(s) of the set of ID wavelengths λ_({ID}) havebeen blocked or passed, allowing the ID block 214 to uniquely identifyoptical link i. The light generated by the light source 220 passesthrough the path A₂-B₂-C₂-D₂-G₂-H₂-I₂ J₂-M₂-N₂-O₂.

In order to perform identification, light returning from the receivingpath (e.g. receiving path i) of an optical link is directed through achannel monitor (e.g. OCM 240). The source optical device 202 may haveone or multiple OCMs to test a set of optical link/s (e.g. optical linki) with remote ID block/s (e.g. remote ID block 216). In someembodiments, the OCM 240 is shared between two or more receiving pathssuch that returned ID signals returning over one or more other opticallinks are also directed to the OCM 240. For example, element 244, suchas a splitter element and/or a filter element, directs light from areceiving path that travel over optical link 2 to the OCM 240. In someembodiments, one OCM 240 is shared between all testable optical linkswith remote ID blocks. Alternatively and/or in addition, one or moreadditional OCM elements may be present in one or more connections toother remote ID blocks. The source optical device 202 may includeelectronic circuitry that uses the output of the OCM 240 to performidentification. In some embodiments, the ID block 214 may identify awavelength associated with one or more optical links, one or more portsassociated with a particular wavelength, or other identificationinformation.

In some embodiments, each connection between the source optical device202 and a remote optical device 208 includes a remote monitor block anda monitor block, which may include shared elements. In some embodiments,the ID block may include 214 electrical circuitry, and/or may shareelectrical circuitry and/or resources used by other functionality (e.g.function block 204) of the source optical device 202. In someembodiments, the source optical device 202 includes one or moremicroprocessors (e.g. microprocessor 150) that executes one or morecontrol instructions to carry out one or more identification controlprocesses as described herein. In some embodiments, the remote ID block216 is a passive optical block that includes only passive opticalelements.

In some embodiments, the set of ID signal wavelengths λ_({ID}) mayoverlap with the set of service signal wavelengths λ_({service}), andthe identification mechanism does not operate during normal operation ofthe optical system 200. For example, the identification mechanismdescribed herein may be used during installation, modification, testing,and/or provisioning of the source optical device 202 and the remoteoptical device/s 208. In some embodiments, λ_({ID}) does not overlapwith λ_({service}). When there is no conflict or overlap between the IDwavelengths λ_({ID}) and the service wavelengths λ_({service}), theidentification mechanism may be used during normal operation of thesource optical device 202 and the remote optical device/s 208.

FIG. 4 illustrates an optical system with a monitor block in a sourceoptical device and a remote monitor block in a remote optical device inan example embodiment. The optical system 400 includes a source opticaldevice 402 and a remote optical device 408 connected by an optical linki. A transmission path i from W₄ to X₄ carries service signals from afunction block 404 of the source optical device 402 to a function block412 of the remote optical device 408 over optical link i using light ofa particular service wavelength λ_(i) of a set of service wavelengthsλ_({service}). A receiving path i from Z₄ to Y₄ carries service signalsfrom the function block 412 to the source optical device 402 using λ_(i)light.

The source optical device 402 includes a monitor block 418 that monitorsone or more connections between the source optical device 402 and one ormore remote optical devices 408. The remote optical device 408 includesa remote monitor block 420 that is communicatively coupled with themonitor block 418. As previously noted, a remote monitor block 420 maybe present in one or multiple remote optical devices connected to thesource optical device 402. Furthermore, multiple remote monitor blocksmay be present in a remote optical device 408.

The monitor block 418 transmits monitor signals over transmission path iusing monitor signals of a reference wavelength λ_(r). The monitorsignals are directed into transmission path i at P₄. For example, alight source 422 at Q₄ may generate the monitor signal. In someembodiments, the light source 422 includes one or more broadband lightsources, one or more tunable lasers, one or more diodes such aslight-emitting diodes (LEDs) and laser diodes (LDs), and/or one or moreother light sources that can provide light of the reference wavelengthλ_(r). In some embodiments, the light source 422 is a light source thatexists for another purpose in the source optical device 402, such as alight source that belongs to function block 404. In some embodiments,multiple reference wavelengths and/or dynamically-selected referencewavelengths are used.

In some embodiments, the light source 422 generates λ_(r) light that isdirected into transmission paths that travel over one or more otheroptical links. For example, element 424 may be a switch element and/orsplitter element that transmits light to one or more other transmissionpaths, such as but not limited to a transmission path that travels overoptical link 3, using one or more elements.

The monitor signal is added into the transmission path i correspondingto optical link i at P₄ using one or more elements 426. For example,element 426 may be a multiplexer (MUX) element that combines a servicesignal from the function block 404 with the monitor signal from thelight source 422. The monitor signal travels over a pathQ₄-P₄-C₄-D₄-E₄-F₄-I₄-J₄-K₄-L₄.

At E₄, the monitor signals are directed into a bypass path from E₄ toF₄, such as by using element 432. For example, the bypath path may beset up using WDM techniques, such as by using an optical demultiplexer(DEMUX) element 432 at E₄ and a MUX element 434 at F₄. The DEMUX element432 separates λ_(r) monitor signals at E₄ so that they are not receivedat the function block 412 of the remote optical device 408. The MUXelement 434 adds the λ_(r) monitor signals of wavelength λ_(r) to thereceiving path i at F₄ so that they return to the source optical device402 for processing.

At K₄, one or more optical elements 436-438 direct the monitor signalfrom the receiving path i to a photodetector 440. For example, a DEMUXelement 436 may separate λ_(r) monitor signals wavelength at K₄ anddirect them to the photodetector 440. The redirected monitor signals arenot received at the function block 404 of the source optical device 402.Alternatively, other elements may be used to direct the monitor signalfrom the receiving path i to a photodetector 440. The photodetector 440evaluates returned monitor signal from the remote optical device 408.For example, the photodetector 440 may be used to detect a power of thereturned monitor signal, such as to determine an optical loss on thepath C₄-D₄-E₄-F₄-I₄-J₄. Based on the configuration of the remote monitorblock 420, it may be assumed in one or more embodiments that the opticalloss between D₄ and I₄ is negligible. The connectivity and/or health ofthe optical link i can be compared and continuously monitored. Forexample, the optical loss C₄-D₄ and I₄-J₄ may be compared with baselinedata at factory calibration and/or provisioning. The monitoringmechanism may detect a severe fiber broken event or loss degradationissue during normal operation of the source optical device 402 and theremote optical device 408.

In some embodiments, the photodetector 440 is shared between two or moreoptical links such that monitor signals from one or more other receivingpaths are also directed to the same photodetector 440. For example, anelement 438, such as but not limited to an optical coupler or switchelement, may direct light from a receiving path of optical link 3 to thephotodetector 440. In some embodiments, one photodetector 440 is sharedbetween all monitored optical links with remote ID blocks. Alternativelyand/or in addition, one or more additional photodetector elements may bepresent in one or more connections to other remote monitor blocks.

In some embodiments, each connection between the source optical device402 and a remote optical device includes a remote monitor block and amonitor block, which may include shared elements. In some embodiments,the monitor block 418 may include electrical circuitry, and/or may shareelectrical circuitry and/or resources used by other functionality (e.g.function block 404) of the source optical device 402. In someembodiments, the source optical device 402 includes one or moremicroprocessors (e.g. microprocessor 150) that executes one or morecontrol instructions to carry out one or more monitor control processesas described herein. In some embodiments, the remote monitor block 420is a passive optical block that includes only passive optical elements.

In some embodiments, the monitor mechanism operates during normaloperation of the optical system 400, and the reference wavelength λ_(r)of the monitor signals does not overlap with the wavelengthsλ_({service}) of the service signals. For example, λ_(r) may be outsideof a frequency band selected for the service signals. In someembodiments, more than one reference wavelength is used.

In some embodiments, a source optical device is configured toindependently monitor connectivity and health of a first link component570 used by a transmission path and a second link component 572 used bya receiving path. FIG. 5 illustrates an optical system with a monitorblock for a source optical device and a remote monitor block for aremote optical device in an example embodiment. The optical system 500includes a source optical device 502 and a remote optical device 508connected by an optical link i. A transmission path i from W₅ to X₅carries service signals from function block 504 of the source opticaldevice 502 to the function block 512 of the remote optical device 508.From C₅ to D₅, transmission path i travels over a first link component570 of optical link i, such as a first optical fiber. A receiving path ifrom Z₅ to Y₅ carries service signals from the function block 512 tofunction block 504. From I₅ to J₅, the transmission path i travels overa second link component 572 of optical link i, such as a second opticalfiber. The service signals have a particular service wavelength λ_(i) ofa set of service wavelengths λ_({service}).

The source optical device 502 includes a monitor block 518. One or moreremote monitor blocks 520 may be present in one or multiple opticaldevices connected to the source optical device 502. The monitor block518 transmits monitor signals of a reference wavelength λ_(r) over oneor more optical link components to be monitored. A first circuitincluding monitor block elements 522-530 and remote monitor blockelements 552-554 is configured to monitor transmission path i, and asecond circuit including monitor block elements 532-540 and remotemonitor block elements 556-558 is configured to monitor receiving pathi. In some embodiments, the first circuit and the second circuit operatein the same or similar fashion using elements that perform the same orsimilar functionality with respect to transmission path i and receivingpath i. The first circuit is described in greater detail hereinafter.

In a first circuit associated with transmission path i, a light source528 generates the λ_(r) monitor signals. The monitor signals aredirected into transmission path i corresponding at P₅ using one or moreelements. For example, a WDM element 524 may comprise a MUX element thatadds the λ_(r) monitor signal to the λ_(i) service signal. In someembodiments, the light source 528 includes one or more broadband lightsources, one or more tunable lasers, one or more diodes such aslight-emitting diodes (LEDs) and laser diodes (LDs), and/or one or moreother light sources that can provide λ_(r) light. In some embodiments,the light source 528 is a light source that exists for another purposein the source optical device 502, such as a light source that belongs tofunction block 504. In some embodiments, the light source 528 generatesmonitor signals that are directed into the transmission path of one ormore other optical links. For example, element 522 may be a switchelement and/or splitter element that transmits light to one or moreother transmission paths, such as but not limited to a transmission paththat travels over optical link 3.

In the remote monitor block 520 at the remote optical device 508, themonitor signal enters a bypass path at E₅ using one or more elements.For example, a WDM element 552 may comprise a DEMUX element thatseparates the λ_(r) monitor signals at E₅ so that they are not receivedat function block 512. The WDM element 552 directs the λ_(r) monitorsignals to R₅. At R₅, a reflector 554 reflects the λ_(r) monitor signal.The λ_(r) monitor signal travels back to the WDM element 552, which maycomprise a MUX element that directs the reflected monitor signal back tothe source optical device 502. Although transmission path i isillustrated with arrows indicating a direction of the service signalsfrom W₅ to X₅, the transmission path i allows bidirectional signaling,allowing the reflected monitor signal to travel from the reflector 554at R₅ to the WDM element 524 at P₅. The reflected monitor signal travelsto a photodetector 526 at L₅. For example, a circulator at T₅ may directoutgoing monitor signals from the light source 528 to the WDM 524 viaelement 522, and may direct incoming reflected monitor signals to thephotodetector 526. In some embodiments, a DEMUX element of the WDMelement 524 at P₅ separates the returned monitor signals of wavelengthλ_(r) so that they do not travel to function block 504.

The photodetector 526 detects a power of the reflected monitor signal,such as to determine an optical loss over its path from the light source528 to the photodetector 526,Q₅-T₅-A₅-P₅-C₅-D₅-E₅-R₅-E₅-D₅-C₅-P₅-A₅-T₅-L₅. The source optical device502 may have one or multiple photodetectors 526 to evaluate reflectedmonitor signals. In some embodiments, the photodetector 526 is sharedbetween two or more optical links such that reflected monitor signalsfrom one or more other receiving paths are also directed to the samephotodetector 526. Alternatively and/or in addition, photodetectorelements may be present in one or more other optical links. Based on theconfiguration of the monitor block 518 and the remote monitor block 520,it may be assumed in one or more embodiments that the optical loss onsegments outside of the first link component 570 is negligible. Theconnectivity and/or health of the first link component 570 can becompared and continuously monitored. For example, the opticalmeasurements detected by the photodetector 526 may be compared withbaseline data at factory calibration and/or provisioning to determineoptical loss. The monitoring mechanism may detect a fiber disconnectionor failure event or loss degradation issue in the first link component570 during normal operation of the source optical device 502 and theremote optical device 508.

In some embodiments, the first circuit associated with transmission pathi has additional components to improve health and connectivitymonitoring. For example, a photodetector 530 may be used to monitor thehealth of the light source 528. Light travels from the light source 528to the photodetector 530 without traveling over any optical links. Forexample, light may travel from the light source 528 to the photodetector530 via an element 529, such as but not limited to an optical splitteror switch element that directs light away from the path Q₅-T₅ to thephotodetector 530. The photodetector 530 may determine a current outputof the light source 528 and compare the current output of the lightsource to the baseline data at factory calibration to determine a healthof the light source 528. In some embodiments, the optical measurementsdetected by the photodetector 526 are compared to the current output ofthe light source as detected by the photodetector 530 to determineoptical loss over transmission path i.

In some embodiments, each connection between the source optical device502 and a remote optical device includes a remote monitor block and amonitor block, which may include shared elements.

In some embodiments, the monitor mechanism operates during normaloperation of the optical system 500, and the reference wavelength λ_(r)does not overlap with the wavelengths λ_({service}) of the servicesignals. For example, λ_(r) may be outside of a frequency band selectedfor the service signals. In some embodiments, more than one referencewavelength is used.

In some embodiments, the monitor mechanism operates during normaloperation of the optical system 500, and the wavelength λ_(r) of themonitor signals does not overlap with the wavelengths λ_({service}) ofthe service signals. For example, the reference wavelength λ_(r) may beoutside of a frequency band selected for the service signals. In someembodiments, more than one reference wavelength is used.

In some embodiments, the monitor block 518 may include electricalcircuitry, and/or may share electrical circuitry and/or resources usedby other functionality (e.g. function block 504) of the source opticaldevice 502. In some embodiments, the source optical device 502 includesone or more microprocessors (e.g. microprocessor 150) that executes oneor more control instructions to carry out one or more monitor controlprocesses as described herein. In some embodiments, the remote monitorblock 520 is a passive optical block that includes only passive opticalelements.

An optical add-drop multiplexer (OADM) is an optical device used inwavelength-division multiplexing (WDM) systems for multiplexing androuting different wavelengths of light into or out of a single fiber.This allows multiple communication channels with different wavelengthsto travel over a fiber. An OADM device generally includes an opticaldemultiplexer (DEMUX), an optical multiplexer (MUX), a method ofreconfiguring the paths between the optical demultiplexer and theoptical multiplexer, as well as a set of ports for adding and droppingsignals. OADMs are often used in telecommunications networks. An OADMmay refer to both a fixed optical add-drop multiplexer (FOADM) and/or areconfigurable optical add-drop multiplexer (ROADM).

FIG. 6 illustrates an optical system with an OADM node in an exampleembodiment. The optical system 600 includes a plurality of OADM nodesincluding OADM node 608. The OADM node 608 is coupled to a plurality ofother nodes in the optical system 600 by at least one inter-node opticallink 620-626. An inter-node optical link 620-626 includes at least oneoptical fiber for transmission of multiple wavelength signals in aunidirectional and/or bidirectional manner to and from the OADM node608. Typically, one or more OADM nodes 608 are arranged in a bus, ring,star, mesh, or hybrid topology arrangement. An OADM node 608 may be aterminal node in the optical system 600, such as when the OADM node 608is connected to only one inter-node optical link 620-626.

The OADM node 608 includes at least one direction device 610-616. Adirection device 610-616 routes signals received over a correspondinginter-node optical link 620-626 to other components within the OADM node608, such as but not limited to one or more add-drop group devices602-606 and/or one or more other direction devices 610-616. For example,the OADM node 608 may include one or more express communication linksthat directly transmit and receive service signals between directiondevices 610-616 without adding or dropping any channels.

A direction device 610 may be coupled to one or more add-drop groupdevices 602-606 with one or more optical links. An add-drop group device602-606 may perform add-drop functionality for signals a different setof wavelengths. For example, a particular direction device 610 maycommunicate signals with a first set of wavelengths with a firstadd-drop group device 602, signals with a second set of wavelengths witha second add-drop group device 604, and signals with a third set ofwavelengths with a third add-drop group device 606. In some embodiments,the signals assigned to a particular add-drop group device 60 are asub-band of band of frequencies used by the optical system 600. In someembodiments, an OADM node 608 only has one add-drop group device 602,and a direction device 610-616 transmits the entire band of servicesignals to the single add-drop group device 602.

An add-drop group device 602-606 separates and combines individualchannels of particular wavelengths in the received service signals. Forexample, an add-drop group device 602 may drop or separate signals ofwavelength λ_(x), transmit the λ_(x) signals to a device 628 over anoptical link 630 coupling the device 628 and the add-drop group device602-606, receive λ_(x) signals from the device 628 over the optical link630, and add the received λ_(x) signals to a combined outgoing signalcomprising outgoing signals of multiple wavelengths from one or moreother devices. The device 628 may be an optical device, electricaldevice, and/or electro-optical device. One or more transponders,receivers, transceivers, and/or other optical-electrical andelectrical-optical devices may be employed to communicate with thedevice 628.

The add-drop group device 602 may drop and add signals of a plurality ofwavelengths (such as but not limited to λ_(x)) and may communicateindividual wavelength signals with a plurality of devices (such as butnot limited to device 628). The add-drop group device 602 transmits thecombined signal comprising multiple channels assigned to the add-dropgroup device 602 to one or more direction devices 610-616.

Although the OADM node 608 is illustrated as a logical device, thecomponents of the OADM node 608 may be deployed separately. Add-dropgroup devices 602-606 are often physically deployed separately andindependently from direction devices 610-616. For example, one or moreadd-drop group devices 602-606 may be located in different slots of thesame optical network device shelf as one or more direction devices610-616, one or more different shelves of same network device rack, oneor more different locations at the same site, and/or remotely from asite comprising one or more direction devices 610-616. In someembodiments, one or more add-drop group devices 602-606 are locatedclose to a location of one or more end-users. In some embodiments, oneor more optical links between an add-drop group device 602-606 and adirection device 610-616 go through one or more optical cabling systems,such as but not limited to one or more optical patch panels and/oroptical shuffle boxes.

The direction devices 610-616 may be well equipped with poweredelectrical elements, such as light sources (such as photodiodes, laserdiodes, and/or other light sources) and/or optical channel monitors(OCMs). Furthermore, the direction devices 610-616 may be closely linkeda to powered optical network device and/or network controllers, makingtheir optical connectivity simpler to identify and/or monitor duringprovisioning and/or operation. Alternatively, one or more add-drop groupdevices 602-606 may have complex connection paths to the directiondevices 610-616 and/or other devices in the OADM node 608. Furthermore,one or more add-drop group devices 602-606 may be passive, having noelectrical circuitry and no powered optical element.

FIG. 7 illustrates a direction device and an add-drop group device in anOADM node in an example embodiment. An OADM node 700 includes one ormore direction devices 760 and one or more add-drop group devices 762.The direction device may transmit and receive signals over one or moreoptical links 718-720 with one or more other direction devices (e.g.direction devices 610-616). For clarity in explanation, one directiondevice 760 and one add-drop group device 762 are described in greaterdetail hereinafter; one or more described features may apply to one ormore other direction devices and/or add-drop group devices within theOADM node 700. In some embodiments, one or more direction devices 760are source optical devices (e.g. source optical device 102, 202, 402,502) that include one or more identification blocks and/or one or moremonitor blocks. In some embodiments, one or more add-drop group devices762 are remote optical devices (e.g. remote optical device 108, 208,408, 508) that include one or more remote identification blocks and/orone or more remote monitor blocks. Specific examples are described inFIGS. 8-9 without limiting the disclosure to the example embodiments.

A direction device 760 may include a DEMUX element 704 to separatesignals so that a particular sub-band assigned to a particular add-dropgroup device 762 can be directed to the particular add-drop group device762. The DEMUX element 704 separates service signals of a set ofwavelengths λ_({service}) received over communication link 720 into oneor more signal subsets and transmits the separated signals to one ormore corresponding add-drop group devices 762 over one or more opticallinks 722-726. For example, signals of wavelengths λ_({i}) are directedfrom DEMUX element 704 to add-drop group device 762 over communicationlink 722; signals of wavelengths λ_({j}) are directed from DEMUX element704 to another add-drop group device over communication link 724; andsignals of wavelengths λ_({k}) are directed from DEMUX element 704 toanother add-drop group device over communication link 726.

The direction device 760 may include a MUX element 702 to combinesignals from one or more add-drop group devices (e.g. add-drop groupdevices 602-606) so that the combined signals can be transmitted to oneor more direction devices (e.g. direction devices 610-616) over one ormore communication links 718-720. For example, the MUX element 702 maycombine returned λ_({i}) signals from add-drop group device 762 overcommunication link 722; returned λ_({j}) signals from another add-dropgroup device over communication link 724; and returned λ_({k}) signalsfrom another add-drop group device over communication link 726.

A direction device 760 may include one or more powered electrical and/oroptical elements, such as a pre-amplifier 708, an optical channelmonitor 710, a booster amplifier 706, a photodiode 712, an opticalsupervisory channel 714, a variable optical attenuator, a light source,a power source, electronic circuitry, a processor, and/or otherelements, including powered elements, that can be used by an ID block(e.g. ID block 114, 214) and/or a monitor block (e.g. monitor block 118,418, 518) in one or more embodiments.

In the add-drop group device 762, the DEMUX element 736 separatessignals based on wavelength and directs the separated signals to aplurality of single-wavelength optical links 728-732. Eachsingle-wavelength optical link 728-732 may carry signals of a particularwavelength (e.g. λ_(a), λ_(b), λ_(c)) between the add-drop group device762 and a device (e.g. device 628). The MUX element 734 combinesreturned signals received over the single-wavelength optical links728-732 so that the combined returned signals can be transmitted to thedirection device 760 over communication link 722.

An add-drop group device 762 may be connected to one or multipledirection devices 760. For example, add-drop group device 762 may beconnected to one or more other direction devices (e.g. direction devices610-616) by one or more optical links 752-754. For example, add-dropgroup device 762 may also receive λ_({i}) signals from other directiondevices over optical links 752-754. In some embodiments, signals fromtwo or more direction devices may be directed to the MUX element 734 andthe DEMUX element 736 in an add-drop group device 762. Alternativelyand/or in addition, signals from a direction device may have its own MUXelement 734 and DEMUX element 736. For example, the combined signals mayalso be transmitted from MUX element 734 to one or more other directiondevices over communication links 752-754.

FIG. 8 illustrates a direction device and an add-drop group device in anOADM node that implements an ID mechanism in an example embodiment. AnOADM node 800 includes one or more direction devices 860 and one or moreadd-drop group devices 862. A direction device 860 may transmit andreceive signals over one or more optical links 818-820 to/from one ormore other direction devices (e.g. direction devices 610-616). Forclarity in explanation, one direction device 860 and one add-drop groupdevice 862 are described in greater detail hereinafter; one or moredescribed features may apply to one or more direction devices and/oradd-drop group devices within the OADM node 800. In some embodiments,the OADM node 800, one or more direction devices 860 and/or one or moreadd-drop group devices 862 include one or more elements described withrespect to one or more other embodiments described herein.

The direction device 860 includes one or more ID block components, suchas a light source 850 upstream of DEMUX element 804 and/or a lightsource 856 downstream of DEMUX element 804. The DEMUX element 804separates service signals of a set of wavelengths λ_({service}) receivedover communication link 820 into one or more signal subsets andtransmits the separated signals to one or more corresponding add-dropgroup devices 862 over one or more optical links 822-826.

In the add-drop group device 862, the DEMUX element 836 separatessignals based on wavelength and directs the separated signals to aplurality of single-wavelength optical links 828-832, which may couplethe add-drop group device 862 to one or more devices. The MUX element834 combines returned signals received over the single-wavelengthoptical links 828-832 so that the combined returned signals can betransmitted to the direction device 860 over optical link 822.

The ID signals are added to a transmission path of service signalstransmitted from the direction device 860 to the add-drop group device862. The add-drop group device 862 includes one or more remote ID blockcomponents, such as elements 866-870. For example, element 866 maydirect the ID signals into a bypass path that includes a set of WDMfilters 868, and element 870 may direct the ID signals into a receivingpath for returned service signals from the add-drop group device 862 tothe direction device 860.

In the direction device 860, the returned ID signals are directed to anoptical channel monitor (OCM) 810. The OCM 810 measures properties ofreturned ID signals, such as the wavelength of a particular returned IDsignal. The OCM 810 allows the direction group 860 to determine whichwavelength(s) of the set of ID wavelengths λ_({ID}) have been blocked orpassed, allowing identification of a corresponding optical link 822. Insome embodiments, the OCM 810 receives the returned ID signals after aMUX element 802 combines received signals from one or more add-dropgroup devices 862 over one or more optical links 822-826.

An add-drop group device 862 may be connected to one or multipledirection devices 860. For example, add-drop group device 862 may beconnected to one or more other direction devices (e.g. direction devices610-616) by one or more optical links 852-854. The add-drop group device862 may also receive ID signal and/or service signals from otherdirection devices over optical links 852-854.

In the add-drop group device 862, the bypass path with the set of WDMfilters may be present in each connection path between each directiondevice and each add-drop group device. For example, ID signals fromoptical links 852-854 may pass through elements 866-870, or may passthrough one or more similar set of elements. Furthermore, the bypasspath/s for each direction device of the OADM node 800 may be present inone or more other add-drop group devices of the OADM node 800.

In some embodiments, the direction device 860 includes one or moremicroprocessors (e.g. microprocessor 150) that executes one or morecontrol instructions to carry out one or more identification controlprocesses as described herein. In some embodiments, the add-drop groupdevice 862 is a passive optical device that includes only passiveoptical elements.

FIG. 9 illustrates a direction device and an add-drop group device in anOADM node that implements a monitor mechanism in an example embodiment.An OADM node 900 includes one or more direction devices 960 and one ormore add-drop group devices 962. A direction device 960 may transmit andreceive signals over one or more optical links 918-920 to/from one ormore other direction devices (e.g. direction devices 610-616). Forclarity in explanation, one direction device 960 and one add-drop groupdevice 962 are described in greater detail hereinafter; one or moredescribed features may apply to one or more other direction devicesand/or add-drop group devices within the OADM node 900. In someembodiments, the OADM node 900, one or more direction devices 960,and/or one or more add-drop group devices 962 include one or moreelements described with respect to one or more other embodimentsdescribed herein.

The direction device 960 includes one or more monitor block components,such as a light source 940 for generating monitor signals of a referencewavelength λ_(r). A MUX element 942 may add the λ_(r) monitor signals toone or more service signals, such as a λ_({i}) service signals havingwavelengths in a set of wavelengths assigned to a particular add-dropgroup device 962. The monitor signals added are transmitted from thedirection device 960 to the add-drop group device 962 over optical link922. A same or similar mechanism may add reference signals to servicessignals transmitted to one or more other add-drop group devices over oneor more other optical links 924-926.

The add-drop group device 962 includes one or more remote monitor blockcomponents, such as elements 944-946. For example, element 944 maydirect the monitor signals into a bypass path, such as by using a DEMUXelement 944 to drop the λ_(r) monitor signals from a transmission pathfrom the direction device 960 and a MUX element 946 to add the λ_(r)monitor signals to a receiving path to the direction device 960. Theremaining service signal is processed by the add-drop group device 962,such as by DEMUX element 936 and MUX element 934 to separate signalstransmitted to optical links 928-932 and combine signals received fromoptical links 928-932.

At the direction device 960, the returned λ_(r) monitor signals areevaluated. For example, a DEMUX element 948 may separate λ_(r) monitorsignals from the receiving path and direct them to a photodetector 950.The photodetector 950 evaluates returned monitor signal from add-dropgroup device 962. For example, the photodetector 950 may be used todetect a power of the returned monitor signal, such as to determine anoptical loss over optical link 922.

An add-drop group device 962 may be connected to one or multipledirection devices 960. For example, add-drop group device 962 may beconnected to one or more other direction devices (e.g. direction devices610-616) by one or more optical links 952-954. The add-drop group device962 may also receive monitor signal and/or service signals from otherdirection devices over optical links 952-954.

In the add-drop group device 962, the bypass path may be present in eachconnection path between each direction device and each add-drop groupdevice. For example, monitor signals from optical links 952-954 may passthrough elements 944-946, or may pass through one or more similar set ofelements. Furthermore, the bypass path/s for each direction device ofthe OADM node 900 may be present in one or more other add-drop groupdevices of the OADM node 900.

In some embodiments, the direction device 960 includes one or moremicroprocessors (e.g. microprocessor 150) that executes one or morecontrol instructions to carry out one or more monitor control processesas described herein. In some embodiments, the add-drop group device 962is a passive optical device that includes only passive optical elements.

The specification and drawings are, accordingly, to be regarded in anillustrative rather than a restrictive sense. The sole and exclusiveindicator of the scope of the disclosure, and what is intended by theapplicants to be the scope of the disclosure, is the literal andequivalent scope of the set of claims that issue from this application,in the specific form in which such claims issue, including anysubsequent correction.

In the foregoing specification, embodiments are described with referenceto specific details that may vary from implementation to implementation.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the disclosure. Theexamples set forth above are provided to those of ordinary skill in theart as a complete disclosure and description of how to make and use theembodiments, and are not intended to limit the scope of what theinventor/inventors regard as their disclosure. Modifications of theabove-described modes for carrying out the methods and systems hereindisclosed that are obvious to persons of skill in the art are intendedto be within the scope of the present disclosure and the followingclaims. The sole and exclusive indicator of the scope of the disclosure,and what is intended by the applicants to be the scope of thedisclosure, is the literal and equivalent scope of the set of claimsthat issue from this application, in the specific form in which suchclaims issue, including any subsequent correction.

What is claimed is:
 1. An optical system comprising: a first directiondevice that is a source optical device for an OADM node; a plurality ofadd-drop group devices that are remote optical devices in the OADM node,the plurality of add-drop group devices being configured tocommunicatively couple with the first direction device by a plurality ofoptical links; in the first direction device, at least one light sourcethat generates monitor signals of a reference wavelength; in the firstdirection device, at least one optical element configured to direct themonitor signals into transmission paths from the first direction deviceto one or more of the remote optical devices over the plurality ofoptical links; in each add-drop group device of the plurality ofadd-drop group devices, one or more optical elements that return themonitor signals to the source optical device over a correspondingoptical link; in the first direction device, a photodetector and atleast one optical element configured to direct returned monitor signalsreceived over the plurality of optical links to the photodetector; inthe first direction device, at least one microprocessor configured toexecute control instructions to generate the monitor signals and processone or more outputs of the photodetector in response to the returnedmonitor signals to determine connectivity of the plurality of opticallinks.
 2. The optical system of claim 1, wherein the one or moreadd-drop group devices are passive optical devices.
 3. The opticalsystem of claim 1, wherein determining connectivity of the plurality ofoptical links comprises detecting a fiber disconnection or failure eventon one or more optical links.
 4. The optical system of claim 1, whereindetermining connectivity of the optical links comprises determiningoptical loss over one or more optical links based on baseline data forthe at least one light source.
 5. The optical system of claim 1: whereinthe one or more optical elements at each add-drop group devices includea demultiplexer device in each transmission path from the source opticaldevice and a multiplexer device in each receiving path to the sourceoptical device; wherein the demultiplexer device and the multiplexerdevice direct the monitor signals through a bypass path between eachtransmission path and each receiving path.
 6. The optical system ofclaim 1: wherein the one or more optical elements at each add-drop groupdevice includes a reflector that returns the monitor signals over one ormore transmission optical link components used by one or moretransmission paths; wherein the control instructions, when executed,determine connectivity of one or more receiving optical link components.7. The optical system of claim 1, further comprising: at least oneadditional optical element configured to direct second monitor signalsof the reference wavelength to the remote optical devices over one ormore optical link components used by one or more receiving paths;wherein the one or more optical elements at each add-drop group deviceincludes a second reflector that returns the second monitor signals overthe one or more optical link components used by the one or morereceiving paths; at least one optical element configured to directreturned second monitor signals to a second photodetector; wherein thecontrol instructions, when executed, determine connectivity of one ormore receiving link components.
 8. The optical system of claim 1,further comprising: in the first direction device, a secondphotodetector; wherein determining connectivity of the optical linkscomprises determining optical loss over one or more optical links basedon a current output of the light source as measured by the secondphotodetector.